The problem
When faucets in our house are first used, you get a long wave of hot water from the cold water side. After a while, maybe 1-2 minutes, the water will finally get cold again. And when I say "hot" I mean too hot to touch. Things used to work fine, so this isn't a fundamental screwup in the plumbing.
The plumbing
I have a two-story home with recirculating hot water (dedicated return pipes). The water heater (WH) is in the garage, and was replaced about three years ago. It's a Kenmore 75 gallon unit, and I think our problems started sometime after the WH replacement. Originally, the hot water return went to the recirculating pump, and then into a T-connector on the WH cold input. The first fix attempt (which was well after the new WH was installed) replaced the recirc pump with a Grundfos UP10-16BU ATLC (which has in internal check valve), and replumbed the water return line to enter the WH through the lower drain spigot. This seemed to help a little with our problem, but didn't fix it.
What I've done to diagnose
For all faucets or other appliances that connect to the hot water and have accessible cut-off valves, I tried turning off the hot water to see if that helped. None made any difference. We still have about six bath and shower valves where the pumping is in the wall so I can't turn off the hot side manually. I believe all of them are Delta brand. I also tried unplugging the recirculating pump: this effectively reversed the problem: we'd no longer get hot water from the cold taps, but then we'd get cold from the hot side for a couple minutes. Basically, what you'd expect without recirculation. I've had two plumbers come check out my system. The first "checked" all of my in-wall faucets and declared them to be fine, replaced my hot water recirculating pump, and rerouted the return water line. That didn't fix the problem. The second plumber wanted to install a check valve in series with the pump, but since the pump has an internal check valve I wouldn't let him. I became suspicious that we were getting convection (thermal) mixing, so I had plumber #2 put a 8-inch vertical rise and fall in the cold water input to the WH (like an upside-down sink trap; I think this is called a heat trap). But that made no difference.
Both plumbers suggested putting in a cold water check valve to prevent backflow from the WH, but I'm reluctant to do this. For one thing, I believe CA plumbing code requires that I also install a thermal expansion tank, which is extra cost, annoyance, and potential maintenance hassle. But more importantly, everything used to work fine without a cold water check valve. There should be no way for hot water to be pumped through the cold water system, unless I have some crossover connection between my hot and cold lines.
Ideas? Can Delta mixer valves leak from hot-to-cold without water coming out of the fixture?
When faucets in our house are first used, you get a long wave of hot water from the cold water side. After a while, maybe 1-2 minutes, the water will finally get cold again. And when I say "hot" I mean too hot to touch. Things used to work fine, so this isn't a fundamental screwup in the plumbing.
The plumbing
I have a two-story home with recirculating hot water (dedicated return pipes). The water heater (WH) is in the garage, and was replaced about three years ago. It's a Kenmore 75 gallon unit, and I think our problems started sometime after the WH replacement. Originally, the hot water return went to the recirculating pump, and then into a T-connector on the WH cold input. The first fix attempt (which was well after the new WH was installed) replaced the recirc pump with a Grundfos UP10-16BU ATLC (which has in internal check valve), and replumbed the water return line to enter the WH through the lower drain spigot. This seemed to help a little with our problem, but didn't fix it.
What I've done to diagnose
For all faucets or other appliances that connect to the hot water and have accessible cut-off valves, I tried turning off the hot water to see if that helped. None made any difference. We still have about six bath and shower valves where the pumping is in the wall so I can't turn off the hot side manually. I believe all of them are Delta brand. I also tried unplugging the recirculating pump: this effectively reversed the problem: we'd no longer get hot water from the cold taps, but then we'd get cold from the hot side for a couple minutes. Basically, what you'd expect without recirculation. I've had two plumbers come check out my system. The first "checked" all of my in-wall faucets and declared them to be fine, replaced my hot water recirculating pump, and rerouted the return water line. That didn't fix the problem. The second plumber wanted to install a check valve in series with the pump, but since the pump has an internal check valve I wouldn't let him. I became suspicious that we were getting convection (thermal) mixing, so I had plumber #2 put a 8-inch vertical rise and fall in the cold water input to the WH (like an upside-down sink trap; I think this is called a heat trap). But that made no difference.
Both plumbers suggested putting in a cold water check valve to prevent backflow from the WH, but I'm reluctant to do this. For one thing, I believe CA plumbing code requires that I also install a thermal expansion tank, which is extra cost, annoyance, and potential maintenance hassle. But more importantly, everything used to work fine without a cold water check valve. There should be no way for hot water to be pumped through the cold water system, unless I have some crossover connection between my hot and cold lines.
Ideas? Can Delta mixer valves leak from hot-to-cold without water coming out of the fixture?